Binary Tree Level Order Traversal
MediumP1Coding
Given the root of a binary tree, return its level-order traversal: the node values level by level, from left to right, as a list of lists. An empty tree gives an empty list.
Tree nodes have val, left and right. The class TreeNode is already defined for you. The tree arrives in level-order form (as in the examples) and you receive its root, which is null for an empty tree.
Example 1
- Input
- root = [3,9,20,null,null,15,7]
- Output
- [[3],[9,20],[15,7]]
Example 2
- Input
- root = [1]
- Output
- [[1]]
Example 3
- Input
- root = []
- Output
- []
Constraints
- The number of nodes is in the range [0, 2000].
- -1000 <= Node.val <= 1000
Hints
Give it a real attempt first. Run shows which examples fail.
Saved automatically
Run checks the 3 visible tests, Submit all 9. ⌘Enter runs, ⌘⇧Enter submits.